What Is Human Chorionic Gonadotropin (hCG)?

Human chorionic gonadotropin, commonly known as hCG, is a hormone found in blood and urine throughout pregnancy. HCG becomes detectable in blood shortly after implantation of the embryo in the uterus (roughly three weeks into a four-week menstrual cycle). Increasing levels of hCG tell the body that you are pregnant, putting the womb to work creating a safe home for your baby to grow in.

Why hCG Is Important

When an embryo forms, it begins making hCG, which facilitates the production of other important pregnancy hormones like progesterone and estrogen. This causes the lining of the uterus to thicken and increase its blood supply, so it can receive the embryo and feed it after implantation. The correct balance of these essential hormones is key for a healthy pregnancy and development of your baby.

Pregnancy Tests

Home pregnancy tests work by finding hCG in the urine. In early pregnancy, the detectable levels of hCG should double roughly every two days. The hormone can be detected in the urine around the time of the first day of a missed menstrual period. For optimal accuracy, wait a few days after a missed period before taking a pregnancy test. A urine test can only tell you whether or not there is hCG in the body, not how much there is.

In early pregnancy, doctors might use one of two types of blood tests to check hCG levels. The most common is a quantitative hCG blood test, which determines how much hCG is in the blood. The measurement is reported in units called milli-international units of hCG per milliliter of blood (mIU/mL).

Pregnancy Complications

HCG levels are instructive in alerting doctors to possible pregnancy complications, including miscarriage. People whose hCG levels fall over a period of two to three days in the first trimester in two quantitative hCG blood tests are often advised that this signals an impending miscarriage. This is especially true for people with other miscarriage symptoms, such as vaginal bleeding.

Decreasing hCG levels later in pregnancy, such as in the second and third trimester, are probably not a cause for concern. Most doctors do not check quantitative hCG levels for purposes of evaluating the progress of a pregnancy after the first trimester, although single hCG levels might be checked as a part of the alpha-fetoprotein (AFP) prenatal screening test, which looks for possible birth defects.

Uses for hCG

This hormone can also be taken as prescription medicine for multiple uses, primarily relating to fertility treatments. HCG is approved by the Food and Drug Administration (FDA) for the treatment of female infertility and other medical uses. It's also marketed for weight loss, but it's not approved for that purpose.

Fertility Treatments

HCG may be prescribed to boost sperm production. It can also prompt ovulation, and is often used in conjunction with scheduled intercourse and other fertility treatments, such as intrauterine insemination (IUI) and in vitro fertilization (IVF). Studies show that taking hCG can increase pregnancy rates and the success of many fertility procedures.

For female fertility treatments, you may receive pre-filled hCG syringes (or ones that you prepare yourself) to inject at home before or after intercourse and/or fertility treatments. Your doctor will provide detailed instructions on when and how to administer these shots. It's important that hCG only be taken as prescribed and directed by your physician.

Weight Loss Products

HCG has not been approved for weight loss or for any other over-the-counter uses. However, there are numerous untrue and misleading claims out there that hCG works for weight loss—and numerous hCG supplements are marketed using these spurious claims. Do not buy them, as there is no credible evidence to back up these assertions. In fact, the FDA calls these products "dangerous" and "unhealthy."

What to Know About hCG Testing

If you are having your hCG levels tested, you'll want to have a general sense of what to expect and how results are interpreted. Most importantly, while general ranges provide an idea of what is "normal," the results of one hCG blood test mean very little. The change in the level between two consecutive tests done two to three days apart is much more telling about how a pregnancy is progressing.

Quantitative Tests

Quantitative hCG blood tests can provide useful information about miscarriage symptoms in the first few weeks after conception. Comparing levels from two quantitative hCG blood tests to look at the hCG doubling time over two to three or more days can give a strong indication of whether or not the pregnancy is progressing as it should be at that point in time.

Qualitative Tests

Doctors may also use qualitative hCG blood tests. These simply return a yes or no answer on whether or not there is hCG in the blood. As hCG levels begin to rise after implantation of an embryo, this test gives you a good sense of whether that has happened. It does not tell you how much hCG is in your system or if it is rising or falling, just if there is a detectable amount of the hormone in your blood.

A Word From Verywell

For the most part, during routine pregnancies, the main time you'll be interested in your hCG levels is when you take your pregnancy test. Otherwise, assuming the pregnancy develops optimally, there's nothing you need to do or pay attention to regarding your hCG levels.

On the other hand, when fertility issues are at play and/or when you want to know whether or not a pregnancy is progressing normally, monitoring hCG levels can be instrumental in helping you know what's going on—and getting pregnant.